This invention generally relates to inkjet printing. More particularly, this invention relates to the sealing and assembly of a container used to store and deliver ink to an inkjet printhead, by which the invention provides a robust solution to needs for today's products, such as replacing or repairing ink delivery systems.
Many printers today use inkjet pens to produce recorded media. The inkjet pens have a container used to store and deliver ink to the printhead. The containment of the ink is usually done at a partial vacuum in the range of 0.5 to 9.0 inches of water column to prevent leakage of ink from the printhead. It is undesirable to allow ink to penetrate a seal between different pen parts that create this containment body. Likewise, it is also undesirable to allow air to intrude the containment body through the seal. In addition, the seal technique used should not be permitted to degrade the ink within the container, such as by the seal corroding due to a reaction with the ink. To allow for easy maintenance of assembly processes, it is desirable to have the sealing function be highly consistent and reliable in its manufacture. An additional feature desired in a seal design is the ability to seal, unseal and reseal without degradation of the seal's properties. This feature would permit new processes to be used to repair or modify an inkjet pen.
One current approach to sealing members on inkjet pens is to use an adhesive. However, most adhesives and their resultant seals degrade when exposed to the ink. In addition, many adhesives have also been shown to contaminate the ink. Other manufacturing problems are related to the time it takes adhesives to cure, thus limiting throughput, and the inconsistency of seals on separate containers due to the variation of adhesive formulations from lot to lot. Although using heat can accelerate the curing time of an adhesive, the heat often causes other parts of the pen to become damaged. In addition, damage to the sealing members occurs when the adhesive joint is broken, thus preventing one from repairing a malfunctioning inkjet pen.
Ultrasonic welding is a second approach used on contemporary inkjet pens to seal members. This technique requires the materials of the two parts being sealed to be ultrasonically compatible which is not always desirable or even possible for a given application. The high frequency energy, used to heat and melt the plastic, often causes damage to other parts of the pen. To perform the ultrasonic welding properly, the parts need to be precisely supported during the weld thereby requiring expensive tooling fixtures. In addition, to ensure consistency and quality of the weld joints, there must be significant planarity between the welding surfaces, which requires tight part tolerances, thus making them more expensive. Many times energy directors are molded into the plastic to increase the likelihood of welding a good seal. These energy directors are usually delicate part features that are easily damaged. Once an ultrasonic seal is broken, it is virtually impossible to reseal properly and this prevents repairing a malfunctioning inkjet pen.
A third approach used is a face seal gasket between the mating parts. The face seal gasket requires that the mechanical joining function of the mating parts react to a constantly applied load from the face seal gasket. This force requires the surfaces on each side of the face seal gasket be smooth and rigid, thus increasing the part cost. In addition, there must be a continuous attachment mechanism or one that has frequent points of attachment to keep the joining surfaces flat. If the attachment mechanisms are exposed to the ink, they may degrade. In addition, if there is a preexisting stress in an attachment point, it may fail after a prolonged period in which it has been subjected to the gasket force, thus causing an early failure of the seal.
There is a need for an attachment and sealing process that is suitable for low cost, high volume manufacturing processes such as those used in assembling inkjet pens. A new seal design must allow for less expensive components, more efficient processes, and high volume manufacturing that provides better consistency, quality and reliability of the finished product. The ability to make repeated seals and reseals without degradation would allow an inkjet pen to be repaired or modified. Furthermore, a new seal design also needs to: allow for parts having looser tolerances; withstand attack from many different types of ink; allow for the attachment joint to not be in contact with the ink; and be virtually independent to the use of different plastic molding material. Other concerns a new seal design should address are: saving capital tooling costs required to build production lines, minimizing the size of production lines, and preventing process induced damage to other parts of the pen which might go undetected during manufacturing and later become field failures.